1. Field of the Disclosure
The disclosure relates generally to image forming devices, and, more particularly, to a photoconductor unit for forming an image on a media sheet in an image forming device.
2. Description of the Related Art
Media processing devices, such as printing devices, are typically used to output information displayed on a screen of a data processing device, such as a personal computer. The information may be output on a media sheet, such as a sheet of paper. Printing devices, such as electrophotographic printers, operate by generating an image pattern of information to be printed, and, subsequently transfer toner particles onto a media sheet based on the generated image pattern to produce the image of the information on the media sheet.
An electrophotographic printer typically includes a photoconductor unit for generating the image pattern. The photoconductor unit includes a photoconductor drum and a charge roller. The charge roller is used to charge a surface of the photoconductor drum to a predetermined voltage. A light source, such as a laser diode, may be provided in the electrophotographic printer for emitting a light beam which is pulsed on and off as it is swept across the surface of the photoconductor drum to selectively discharge the surface of the photoconductor drum. A toner unit including a developer roller and a toner medium is provided for developing the image pattern on the surface of the photoconductor drum. Charged toner particles of the toner medium are electrostatically attracted to a surface of the developer roller and are metered into a uniform layer by a metering device such as a doctor blade. As the developer roller rotates, the toner particles on the surface of the developer roller are attracted and move onto the discharged surface areas on the photoconductor drum. In this way, a toned image pattern develops on the surface of the photoconductor drum. The toned image pattern may then be transferred onto a media sheet for forming an image onto the media sheet. A fuser nip may be configured in the electrophotographic printer for receiving the media sheet having the toned image thereon and is used to permanently affix or fuse the toner particles onto the media sheet using heat and or pressure. The media sheet with the affixed toner particles forming the image may then be exited from the electrophotographic printer.
The charge roller of the photoconductor unit may be configured to linearly move, towards and away, from the photoconductor drum for assuming a working position and a storage position, respectively. More specifically, in the working position, the charge roller contacts the photoconductor drum for charging the photoconductor drum. In the storage position, the charge roller linearly retracts away from the photoconductor drum. While transferring the toner particles onto the media sheet, some amount of the toner particles may remain on the surface of the photoconductor drum. These remnant toner particles may adhere onto the charge roller when the charge roller charges the photoconductor drum. The remnant toner particles on the charge roller may result in an uneven charging of the photoconductor drum which can degrade print quality of the image printed on the media sheet.
Further, the photoconductor unit of the media processing device, such as the above-mentioned electrophotographic printer, typically includes a cleaning blade for precluding transfer of the remnant toner particles onto the charge roller from the photoconductor drum. However, these remnant toner particles may adhere to the cleaning blade and wear a portion of the surface of the photoconductor drum. The remnant toner particles may accumulate in that portion of the surface and may further contaminate the charge roller.
To this end, a charge roller wiper adapted to clean a surface of the charge roller may be configured within the photoconductor unit. A photoconductor unit configured with a typical charge roller wiper is depicted in FIG. 1.
Referring now to FIG. 1, a side view of a photoconductor unit 10 including a prior art charge roller wiper arrangement adapted for cleaning a surface of a charge roller 12 is depicted. Charge roller wiper arrangement 10 includes a charge roller wiper 14 which corresponds in length to the length of the charge roller and peripherally contacts charge roller 12. As illustrated charge roller wiper 14 is rectangular in cross section. Charge roller 12 is depicted to be in the working position in FIG. 1. A developer roller 16 of a toner unit (not shown) is further depicted in FIG. 1. Developer roller 16 provides toner particles to a surface of a photoconductor drum 18 for forming an image pattern on the surface. Charge roller wiper 14 is supported on a support bracket 20 and removes remnant toner particles transferred onto charge roller 12 from the surface of photoconductor drum 18. In the storage position, charge roller 12 linearly retracts away from photoconductor drum 18 along line XX′, further compressing charge roller wiper 14 in a central region that is also used for wiping charge roller 12. Charge roller wiper 14 slowly decompresses from the compressed state when charge roller 12 assumes the working position.
Typically, a time delay is incurred when charge roller wipers, such as charge roller wiper 14, try to recover from the compressed state to the decompressed state. Height recovery rate, i.e., rate of recovering of a height of a charge roller wiper from a compressed state to a decompressed state is explained in conjunction with FIG. 2.
FIG. 2 depicts variation in height recovery rates of four exemplary charge roller wipers, while recovering from the compressed state to the decompressed state. Plots 22, 24, 26 and 28, depicted in FIG. 2, represent variation in recovery of a height of each of the exemplary four charge roller wipers with respect to time. The recovery of the height of each of the four charge roller wipers is expressed as a percentage of original non-compressed heights of the respective charge roller wipers. The variation in time is expressed in hours. The four charge roller wipers are initially compressed, reducing the height of each of the four charge roller wipers by 1 millimeter (mm) or approximately 25% (typical wipers have a height of about 4.1 mm±0.3 mm) and, placed in an environment having an atmospheric temperature of about 70° C. and a relative humidity of about 50%. Thereafter, the compressed four charge roller wipers may be placed in an environment having an atmospheric temperature of about 22° C. and allowed to attain the decompressed state from the compressed state. Accordingly, plot 22 shows an initial compression of a height of a first charge roller wiper of the four charge roller wipers to about 21% of its original height. Thereafter, on being allowed to attain a decompressed state, the first charge roller wiper attains about 83% of its original height in a time span of 24 hours, as depicted by plot 22.
Similarly, plots 24, 26 and 28 depict an initial compression of heights of a second charge roller wiper, a third charge roller wiper and a fourth charge roller wiper of the four charge roller wipers to about 20%, 21% and 24% of their original heights, respectively. Thereafter, while attaining the decompressed state, the second charge roller wiper, the third charge roller wiper and the fourth charge roller wiper attain about 83%, 82% and 80% of their original heights, respectively, in the time span of 24 hours. Further, as evident from FIG. 2, plots 22, 24, 26 and 28 are logarithmic, i.e., the height recovery of the four charge roller wipers after 24 hours is not as a rapid as the height recovery after the first day. Thus, the four charge roller wipers may not re-attain their original heights during their useable lifetimes due to the moment of the charge roller between its working and storage positions.
The time delay in recovering from the compressed state to the decompressed state, delays cleaning of a charge roller when the charge roller assumes the working position, thereby degrading the cleaning efficiency of the charge roller. Moreover, effective cleaning of the charge roller depends upon factors such as a surface area of contact of the charge roller wiper with the charge roller, a cleaning force applied by the charge roller wiper on the charge roller, and a capacity of the charge roller wiper to retain contamination. Throughout an operating life term of a photoconductor unit, the charge roller wiper may attain the compressed state multiple times thereby leading to a permanent deformation, also known as a plastic deformation, of the charge roller wiper, reducing the contact force of the charge roller wiper on the surface of the charge roller. Moreover, atmospheric conditions such as increased pressure, heat and humidity may accelerate the permanent deformation of the charge roller wiper, thereby reducing the surface area of contact of the charge roller wiper with the charge roller also reducing the cleaning force applied to the charge roller. Thus, effective cleaning of the charge roller by the charge roller wiper may be affected on account of compression of the charge roller wiper, thereby causing print defects, such as vertical and top-to-bottom streaks on a media sheet processed by the media processing device.
Based on the foregoing, there is a need for effectively cleaning a charge roller in an image forming device. Further, there exists a need for precluding a time delay in cleaning of a charge roller on assuming the working position by the charge roller. Furthermore, there exists a need for effectively cleaning a charge roller for precluding development of vertical and top-to-bottom streaks on a media sheet processed by the media processing device.